CreateFile in separate thread returns INVALID_HANDLE_VALUE in MFC app

Question

I have an MFC App which fires up a separate thread for downloading some files via cURL. At the start it downloads a text file with file sizes and last write times. Then it checks the files on disk and queues it for downloading if it has different values.. The problem is; the CreateFile call in the thread arbitrarily returns INVALID_HANDLE_VALUE. I always do CloseHandle() after a successful CreateFile(). The failing files are just random. Sometimes a file in the root dir, another time a file in a nested directory. The problem is not related to localization or directory/file names since sometimes all checks pass but sometimes don't. GetLastError() return 2 or 3 on occasion which are "File not found" / "Path not found" respectively.

When I put the function checking the file write times and size straight into the OnInitDialog() function, everything works. This smells like a multithreading issue but I double-checked everything from memory allocations to file handles.

The same code works in a console application also in a separate thread.

The platform is Win7 64bit.
Linking statically to the runtime and MFC.

Are you using absolute paths or relative paths? Maybe another thread is changing the current directory, causing your relative paths to go invalid. — Raymond Chen, Oct 31 '11 at 14:16
I can not thank you enough... :) Make it an answer so I can up it. — fgungor, Oct 31 '11 at 14:43

score 1 · Accepted Answer · answered May 10 '12 at 08:04

in my case GetCurrentDirectory() returned the system32 path after some time so my code failed because of credentials. I fixed the issue by determining file paths manually (getting the exe path at the start and use it from there on...) . Make sure you are not trying to write to/read from a privileged location on disk. Check your paths.

CreateFile in separate thread returns INVALID_HANDLE_VALUE in MFC app

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